/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 *
 */

package java.io;

/**
 * A <code>ByteArrayInputStream</code> contains
 * an internal buffer that contains bytes that
 * may be read from the stream. An internal
 * counter keeps track of the next byte to
 * be supplied by the <code>read</code> method.
 * <p>
 * Closing a <tt>ByteArrayInputStream</tt> has no effect. The methods in
 * this class can be called after the stream has been closed without
 * generating an <tt>IOException</tt>.
 *
 * @author Arthur van Hoff
 * @see java.io.StringBufferInputStream
 * @since JDK1.0
 */
public class ByteArrayInputStream extends InputStream {

  /**
   * An array of bytes that was provided
   * by the creator of the stream. Elements <code>buf[0]</code>
   * through <code>buf[count-1]</code> are the
   * only bytes that can ever be read from the
   * stream;  element <code>buf[pos]</code> is
   * the next byte to be read.
   */
  protected byte buf[];

  /**
   * The index of the next character to read from the input stream buffer.
   * This value should always be nonnegative
   * and not larger than the value of <code>count</code>.
   * The next byte to be read from the input stream buffer
   * will be <code>buf[pos]</code>.
   */
  protected int pos;

  /**
   * The currently marked position in the stream.
   * ByteArrayInputStream objects are marked at position zero by
   * default when constructed.  They may be marked at another
   * position within the buffer by the <code>mark()</code> method.
   * The current buffer position is set to this point by the
   * <code>reset()</code> method.
   * <p>
   * If no mark has been set, then the value of mark is the offset
   * passed to the constructor (or 0 if the offset was not supplied).
   *
   * @since JDK1.1
   */
  protected int mark = 0;

  /**
   * The index one greater than the last valid character in the input
   * stream buffer.
   * This value should always be nonnegative
   * and not larger than the length of <code>buf</code>.
   * It  is one greater than the position of
   * the last byte within <code>buf</code> that
   * can ever be read  from the input stream buffer.
   */
  protected int count;

  /**
   * Creates a <code>ByteArrayInputStream</code>
   * so that it  uses <code>buf</code> as its
   * buffer array.
   * The buffer array is not copied.
   * The initial value of <code>pos</code>
   * is <code>0</code> and the initial value
   * of  <code>count</code> is the length of
   * <code>buf</code>.
   *
   * @param buf the input buffer.
   */
  public ByteArrayInputStream(byte buf[]) {
    this.buf = buf;
    this.pos = 0;
    this.count = buf.length;
  }

  /**
   * Creates <code>ByteArrayInputStream</code>
   * that uses <code>buf</code> as its
   * buffer array. The initial value of <code>pos</code>
   * is <code>offset</code> and the initial value
   * of <code>count</code> is the minimum of <code>offset+length</code>
   * and <code>buf.length</code>.
   * The buffer array is not copied. The buffer's mark is
   * set to the specified offset.
   *
   * @param buf the input buffer.
   * @param offset the offset in the buffer of the first byte to read.
   * @param length the maximum number of bytes to read from the buffer.
   */
  public ByteArrayInputStream(byte buf[], int offset, int length) {
    this.buf = buf;
    this.pos = offset;
    this.count = Math.min(offset + length, buf.length);
    this.mark = offset;
  }

  /**
   * Reads the next byte of data from this input stream. The value
   * byte is returned as an <code>int</code> in the range
   * <code>0</code> to <code>255</code>. If no byte is available
   * because the end of the stream has been reached, the value
   * <code>-1</code> is returned.
   * <p>
   * This <code>read</code> method
   * cannot block.
   *
   * @return the next byte of data, or <code>-1</code> if the end of the stream has been reached.
   */
  public synchronized int read() {
    return (pos < count) ? (buf[pos++] & 0xff) : -1;
  }

  /**
   * Reads up to <code>len</code> bytes of data into an array of bytes
   * from this input stream.
   * If <code>pos</code> equals <code>count</code>,
   * then <code>-1</code> is returned to indicate
   * end of file. Otherwise, the  number <code>k</code>
   * of bytes read is equal to the smaller of
   * <code>len</code> and <code>count-pos</code>.
   * If <code>k</code> is positive, then bytes
   * <code>buf[pos]</code> through <code>buf[pos+k-1]</code>
   * are copied into <code>b[off]</code>  through
   * <code>b[off+k-1]</code> in the manner performed
   * by <code>System.arraycopy</code>. The
   * value <code>k</code> is added into <code>pos</code>
   * and <code>k</code> is returned.
   * <p>
   * This <code>read</code> method cannot block.
   *
   * @param b the buffer into which the data is read.
   * @param off the start offset in the destination array <code>b</code>
   * @param len the maximum number of bytes read.
   * @return the total number of bytes read into the buffer, or <code>-1</code> if there is no more
   * data because the end of the stream has been reached.
   * @throws NullPointerException If <code>b</code> is <code>null</code>.
   * @throws IndexOutOfBoundsException If <code>off</code> is negative, <code>len</code> is
   * negative, or <code>len</code> is greater than <code>b.length - off</code>
   */
  public synchronized int read(byte b[], int off, int len) {
    if (b == null) {
      throw new NullPointerException();
    } else if (off < 0 || len < 0 || len > b.length - off) {
      throw new IndexOutOfBoundsException();
    }

    if (pos >= count) {
      return -1;
    }

    int avail = count - pos;
    if (len > avail) {
      len = avail;
    }
    if (len <= 0) {
      return 0;
    }
    System.arraycopy(buf, pos, b, off, len);
    pos += len;
    return len;
  }

  /**
   * Skips <code>n</code> bytes of input from this input stream. Fewer
   * bytes might be skipped if the end of the input stream is reached.
   * The actual number <code>k</code>
   * of bytes to be skipped is equal to the smaller
   * of <code>n</code> and  <code>count-pos</code>.
   * The value <code>k</code> is added into <code>pos</code>
   * and <code>k</code> is returned.
   *
   * @param n the number of bytes to be skipped.
   * @return the actual number of bytes skipped.
   */
  public synchronized long skip(long n) {
    long k = count - pos;
    if (n < k) {
      k = n < 0 ? 0 : n;
    }

    pos += k;
    return k;
  }

  /**
   * Returns the number of remaining bytes that can be read (or skipped over)
   * from this input stream.
   * <p>
   * The value returned is <code>count&nbsp;- pos</code>,
   * which is the number of bytes remaining to be read from the input buffer.
   *
   * @return the number of remaining bytes that can be read (or skipped over) from this input stream
   * without blocking.
   */
  public synchronized int available() {
    return count - pos;
  }

  /**
   * Tests if this <code>InputStream</code> supports mark/reset. The
   * <code>markSupported</code> method of <code>ByteArrayInputStream</code>
   * always returns <code>true</code>.
   *
   * @since JDK1.1
   */
  public boolean markSupported() {
    return true;
  }

  /**
   * Set the current marked position in the stream.
   * ByteArrayInputStream objects are marked at position zero by
   * default when constructed.  They may be marked at another
   * position within the buffer by this method.
   * <p>
   * If no mark has been set, then the value of the mark is the
   * offset passed to the constructor (or 0 if the offset was not
   * supplied).
   *
   * <p> Note: The <code>readAheadLimit</code> for this class
   * has no meaning.
   *
   * @since JDK1.1
   */
  public void mark(int readAheadLimit) {
    mark = pos;
  }

  /**
   * Resets the buffer to the marked position.  The marked position
   * is 0 unless another position was marked or an offset was specified
   * in the constructor.
   */
  public synchronized void reset() {
    pos = mark;
  }

  /**
   * Closing a <tt>ByteArrayInputStream</tt> has no effect. The methods in
   * this class can be called after the stream has been closed without
   * generating an <tt>IOException</tt>.
   */
  public void close() throws IOException {
  }

}
